Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains generally to chemical treatment systems, and more particularly to a modular point of use chemical treatment system that permits individual treatment of specific chemical process mixtures.
2. Description of the Background Art
Several point-of-use chemical treatment systems are commercially available which utilize thermal, wet scrubbing, dry scrubbing, catalytic, or plasma technologies. However, the current implementations of these technologies tend to suffer from poor economic feasibility or low chemical treatment efficiency due to the need for multiple and simultaneous treatment of specific chemical process mixtures. Many equipment manufacturers accommodate the need for process specific treatment solutions by offering several different products, based upon different technology implementations, that provide solutions for individual specific process mixtures and not for multiple process mixtures. Because of the vast number of different process streams that may need to be treated, a commensurate number of standalone abatement technologies and systems have been developed, most notably those that are described in the following discussion.
Thermal reactors utilize a variety of means to heat chemical process mixtures to high equilibrium temperatures. In addition, reagent gases are added to promote specific reaction chemistries; for example, oxygen or air can be added to promote oxidation. The chemical process mixture can be heated upon contact with a hot surface or through mixing with hot gas. However, hot surface reactors are greatly susceptible to corrosion failure and material accumulation leading to clogging. Common hot gas reactors utilize combustion to heat and react the chemical process mixture in the gas phase. Combustion systems are extremely sensitive to fuel gas and oxidizing gas control and mixing. Corrosion and material accumulation on injection nozzles and igniters result in degraded performance of these systems unless frequent maintenance is performed. A significant expense and liability associated with combustion systems is the piping of fuel gas (specific to the combustion reactor) throughout the manufacturing facility to permit equipment installation.
Glow discharge plasmas are capable of depositing much of their applied power into the gaseous medium to achieve a high percentage of ionization or dielectric breakdown. Such devices operating with electrode potentials of several hundred volts can deposit several kilowatts of power using high frequency alternating current. Consequently, plasma processes creating energetic electrons, ions, reactive neutrals, and radical species can be promoted in these devices. Complex and diverse plasma chemistries can be conducted, but only at low relative pressures, typically 1 millitorr to 10 torr. Coupling power into the gas stream becomes difficult above these pressures resulting in non-uniform dielectric breakdown and collapse of the plasma region to the electrode (inductively coupled) or electrodes (capacitively coupled) of these devices. Because low pressure operation requires pumping systems, the chemical throughput is directly dependent upon both the scale of the pumping system and the ability to apply high frequency power. In addition, changes to the electrode material or geometry occur as a result of corrosion and material accumulation. Such changes interfere with power coupling to the plasma as a result of detuning and energy dissipation by deposited materials. Chemical processing applications have been limited to low flow gas processing such as chemical vapor deposition, gas phase chemical etching, gas phase spectroscopy, or surface treatment of materials such as fibers and films.
Microwave plasmas are also limited to low pressure operation. As pressures approach 100 torr, the inability to propagate and tune coherent waves limits the ability to deposit energy within a resonant cavity resulting in plasma collapse to the cavity surface. As low pressure operation requires a pumping system, the chemical throughput is again directly dependent upon both the scale of the pumping system and the ability to couple high frequency power. In addition, changes to the cavity material or geometry occur as a result of corrosion and material accumulation. Such changes interfere with power coupling to the plasma by changing the modes of TE and TM fields propagated within the cavity.
Silent discharge plasmas are capable of operating at relatively high gas pressures, typically above one atmosphere. Dielectric breakdown of gases between electrodes with a relatively large separation can be achieved using high voltage potentials. However, such devices require a dielectric barrier between the electrodes and the gas stream to prevent collapse of the plasma due to arcing. The electrical resistance of the dielectric barrier enhances capacitive coupling of power to the plasma, but this resistance also limits the current flow through these devices. While silent discharge plasmas are capable of promoting complex chemistries, plasma chemical activity diminishes dramatically as a function of increased gas flow. Minimizing the dielectric strength of the electrode barrier by placing dielectric material throughout the discharge gap has provided enhanced power deposition, but the complexities of surface reaction chemistries as well as physical fouling are increased. Thus, catastrophic arcing remains the principal failure mode and limiting factor in power deposition within these plasma devices.
Catalytic reactors require moderately high temperatures to promote chemical reactions and desorb reaction products from the catalyst surface. The process gas is preheated by either hot surface contact or gas phase combustion. Therefore, maintenance considerations for the preheating section of the system are similar to those for thermal reactors. Additionally, reaction products can poison the catalyst surface by forming a physical barrier or by chemically bonding to the surface. Where reaction products remain as solids even at high temperatures, physical poisoning occurs. Additionally, locations where reaction products are highly oxidizing or capable of forming stable salts upon reaction with the catalyst, chemical poisoning occurs.
Wet scrubbers require relatively meager amounts of energy for operation since their functionality extends from the inherent chemical affinity between the scrubbing solution and the process gases being treated. Both chemical reactivity and solubility are principle parameters effecting the efficiency and capacity of the scrubbing process. Mass transfer is the physical parameter most important to the efficiency of the scrubbing process. Two primary distinctions are important to properly applying wet scrubbing technology: (1) simple liquid with or without additional reagents, and (2) low energy or high energy. The first distinction dictates the ability to satisfy the chemical parameters for scrubbing when treating specific gases. The second distinction dictates the ability to ensure the requisite physical contact between gaseous or particulate matter and the scrubbing liquid to effect removal. Treatment requirements that create difficulties for wet scrubbers are hazardous process mixtures comprising both gaseous and particulate matter where some of the gases are largely insoluble in the scrubbing liquid such that insufficient reaction occurs with the specific reagents, and particulate having diameters in the nanometer to submicron range is thereby formed prior to, or during, the scrubbing process.
Dry scrubbers vary greatly with regard to energy requirements which range from a simple fixed bed adsorption system having low power consumption levels, to a heated reagent bed having a power consumption which approaches that of a catalytic system. Pressure swing or temperature swing adsorption systems have not been feasible for treating complex and reactive gas mixtures and are, therefore, not discussed. Primary distinctions between various dry scrubbers are physical adsorption, and chemical adsorption. Physical adsorption refers to condensation or molecular trapping processes which occur within the requisite material matrix. Chemical adsorption refers to a combination of physical adsorption and surface chemical reaction processes which bind the molecules of concern to the requisite material matrix. Often chemical adsorption systems require added thermal energy to promote the necessary surface reactions. In both types of dry scrubbers the common concerns are premature clogging of the material matrix by particulate formed upstream, and a limited capacity which requires regular replacement and disposal of the material matrix.
As can be seen, therefore, a number of abatement options are available for the process streams in semiconductor wafer manufacturing. However, the equipment available is generally constructed such that its abatement capabilities are limited to one or two process streams. Industry economics (both cost and space availability) largely dictate that a typical treatment system must simultaneously treat at least four process streams to be feasible. Typical semiconductor wafer manufacturing equipment can simultaneously carry out multiple chemical processing operations. Thus, a single treatment system that is optimized for one or two chemical processes suffers the loss of chemical treatment efficiency and severe maintenance requirements from exposure to the additional chemical process mixtures. Furthermore, because many of the materials requiring treatment are pyrophoric or flammable, serious risk of explosion and fire is associated with poor treatment efficiencies or equipment bypass during unplanned maintenance. Currently, the semiconductor wafer manufacturer is forced to make a compromise in selecting treatment equipment and accept the inherent risk, thus creating a need for a system that is economic, reconfigurable and reliable. The present invention satisfies that need, as well as others, and overcomes deficiencies in current treatment systems.
The present invention comprises a modular point-of-use chemical treatment system employing interchangeable inlet modules which interface to a modular base unit that preferably contains a primary scrubber. In order to optimize individual treatment of specific chemical mixtures and process streams, the inlet modules may be used in combinations, such as by combining high energy reactors, plasma reactors, and scrubbers. The modular system is provided with integrated controls and safety interlocks to permit several different simultaneous unit operations. Reconfiguration of the treatment system, including system expansion, is facilitated through the use of a completely modular subsystem and preferably even the equipment cabinet itself. The modular design of the present invention eliminates the necessity of using an abatement apparatus that is limited to treatment of a particular type of chemical composition or specific process stream.
In accordance with an aspect of the invention, a porous wall thermal reactor which utilizes a thermal process for pyrolizing and oxidizing hazardous materials is provided. A preheated reagent gas is introduced into the thermal reactor through a preferably porous cylindrical reactor wall. Staged mixing of the process gas flowing through the reactor with hot reagent gas causes gas phase reaction of these chemical species, thereby creating new chemical constituents, including gas and particulate matter which are shielded from the reactor wall by the intruding hot reagent gas. These chemical constituents are swept through the reactor and mixed with a cooling gas prior to entering the subsequent scrubbing unit.
In accordance with another aspect of the invention, a falling film plasma reactor which utilizes a high voltage alternating current, or pulsed direct current, is provided. Falling film reactors are typically utilized for reducing metallic oxides, such as Fe2O3, and Fe3O4. The electrical current is applied to radially spaced cylindrical electrodes for creating a dielectric breakdown of the process gas flowing within a large radial gap between the two electrodes. Arcing between the electrodes is prevented by passing a dielectric liquid over the electrodes, or a fixed dielectric barrier over which a conductive or dielectric liquid is caused to flow. A reagent gas introduced into the process gas causes electrical energy deposited into the plasma to dissociate atoms and molecules of the gas stream constituents. Subsequent reaction of these chemical species creates new chemical constituents, including gas and particulate matter which contacts the liquid flowing over the electrodes and is absorbed, or reacted, with the liquid and its constituents. The treated process stream is therein swept through the reactor and mixed with a cooling gas prior to entering the subsequent scrubbing unit.
In accordance with another aspect of the invention, universal cooling air sleeves interface the high energy reactors, or basic scrubber inlet, to a liquid spray chamber containing an integral liquid recirculation pump and drain/sump. The liquid spray chamber includes an outlet flanged to accommodate two distinct types of modular scrubbing units. The first type of scrubbing unit comprises an extended height, high efficiency counter-current, packed bed liquid scrubbing tower which interfaces with the liquid recirculation to provide long residence times and high liquid-to-gas ratios. The second type of scrubbing unit comprises both an abbreviated height, moderate efficiency counter-current, packed bed liquid scrubbing tower which interfaces with liquid recirculation, and a fixed bed dry scrubber with in-situ regeneration capability.
In accordance with yet another aspect of the invention, a basic scrubber inlet that eliminates back mixing of downstream gases is provided. In particular, back mixing is reduced for gases which are introduced into the scrubbing unit from separate process inlets that provide staged mixing of the process gas mixture flowing through the inlet nozzle. The first stage can preferably utilize an inert gas sheath which isolates the inlet nozzle from the gas by increasing the inlet throat diameter to reduce gas velocity. The second stage preferably utilizes a high flow air sheath which isolates the exhaust nozzle from the scrubbing liquid droplets and vapor, such that the resultant process gas mixture, additional nitrogen, and clean dry air, are swept into the subsequent scrubbing unit.
In accordance with still another aspect of the invention, interchangeable particulate collectors are incorporated into the exhaust stream of the scrubbing tower to separate liquid and solid particulates from the exhaust gas stream. Two alternative collector embodiments are preferred for separating the particulates from the exhaust gas. An embodiment of the present invention utilizes a collector comprising a series of impactor plates designed to efficiently remove particle diameters ranging from submicron to low micron. The surfaces of the plates are continuously washed with scrubbing liquid to facilitate particle collection. The second embodiment comprises an air powered ejector which accelerates particles at right angles to a collection surface to thereby effect a removal of particles with diameters in the micron range. The air powered ejector simultaneously enhances the exhaust draw on the modular abatement system and depresses the exhaust gas dew point to minimize downstream vapor condensation.
An object of the invention is to provide a chemical abatement system capable of deployment at the point of use.
Another object of the invention is to provide a modular chemical abatement system that supports several treatment regimens.
Another object of the invention is to optimize individual treatment of specific chemical mixtures.
Another object of the invention is to allow for simultaneous operation of several different treatment units.
Another object of the invention is to provide a system that can be rapidly reconfigured, by the replacement of modules, for a variety of process streams.
Another object of the invention is to provide a system with integrated controls and safety interlocks, whereupon changing the type of modular treatment units, the controls may be set for the proper parameters for the new module, such as flow rate, temperature, and pressure, to optimize system performance.
Another object of the invention is to allow for the coupling of high energy reactors with chemical scrubbing units configured for specific chemical mixtures.
Another object of the invention is to provide an abatement system having a thermal reactor which is capable of pyrolizing and oxidizing hazardous materials.
Another object of the invention is to provide an abatement system utilizing a porous wall thermal reactor in which the buildup of particulate is minimized.
Another object of the invention is to provide an abatement system having a thermal reactor having a porous wall configured for easy cleaning.
Another object of the invention is to provide an abatement system having multistage particulate collectors comprising impactor plate designs and air powered ejectors such that a range of particulate sizes are removed.
Another advantage of the invention is to provide for the recovery of useful chemical compositions and elements, such as Gallium, from the scrubber fluid.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.